Stabilization of nitrocellulose



3,86,897 Patented Apr. 23, 1963 The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.

This application is a continuation-in-part of our application Serial No. 754,117, filed August 8, 1958, entitled Stabilization of Nitrocellulose, now abandoned.

This invention relates to the stabilization of nitrocellulose films, and primarily in their use as containers for propellant for ammunition for recoilless rifles, in the form of liners for cartridge cases, cartridge cases, and as envelopes in the absence of cartridge cases.

When nitrocellulose is stored over long periods of time at ambient temperatures and short periods of time at elevated temperatures, there results a deterioration in chemical and physical properties. Chemically, deterioration takes place, reducing combustibility of the nitrocellulose, which could then result in poor ballistic uniformity of ammunition after long term storage. Physically, the envelope or liner becomes brittle and eventually disintegrates.

The applicants have discovered that certain substituted phenols when added to nitrocellulose in the proper proportion, will substantially retard chemical and physical deterioration of nitrocellulose over long periods of time at ambient and elevated temperatures, while at the same time not in any way reducing the non-corrosive nature of the nitrocellulose liner nor increasing the liner residue after firing.

It is therefore an object of this invention to present a stabilized nitrocellulose which resists chemical and physical deterioration at ambient and elevated temperatures over long periods of time.

In ammunition for recoilless rifles, it has been found that the use of nitrocellulose as a liner for retaining the propellant grains within the cartridge case has improved handling characteristics and is almost completely consumed upon firing of the weapon.

However, it was found that the liners deteriorated when stored at elevated temperatures, l40l65 F. The degradation of the nitrocellulose involves both a denitration process and a polymer chain breakdown. The degradation rate increases with the time because the oxides of nitrogen released serve as catalysts for further decomposition.

Diphenylamine has long been used as an additive for the stabilization of nitrocellulose base propellants. The propellants, with diphenylamine added, have shown good shelf life. However, diphenylamine itself is reputed to have a deleterious effect on nitrocellulose. Therefore, although widely used for stabilizing nitrocellulose base propellants, it was felt that diphenylamine might not be satisfactory as a stabilizer of nitrocellulose film. In using diphenylamine as a standard of comparison, however, it was found that it could be used as a stabilizer for nitrocellulose film, but other compounds were discovered which are as good as, or superior to, diphenylamine.

Various concentrations were tested, with the result that about 0.5 to 3% by weight of additive, to weight of nitrocellulose appeared to be the use concentration range imparting effective stabilization. 2- and 4-phenylphenol, 2- and 4-benzyloxyphenol, 4,4'-, 2,4-, 2,2'-dihydroxydiphenyl and 2,5-di-t-butylhydroquinone were preferred among the substituted phenols considered. It appears that better results can be obtained with the benzyloxyphenol if its concentration is increased slightly to about 1 to 4%.

To further clarify our invention, our film compositions were prepared in the following manner: Approximately 20% by weight of dry nitrocellulose was dissolved in a solvent, such as methyl ethyl ketone, for example. The additive was dissolved in a small amount of the selected solvent and thoroughly blended with the nitrocellulose solution. The following typical stabilized nitrocellulose film formulas are given by way of illustration:

Example I Gms.

Nitrocellulose 200 Methyl ethyl ketone 800 2,4-dihydroxydiphenyl, or 4,4-dihydroxydiphenyl or 2,2-dihydroxydiphenyl dissolved in 25 cc. meth- In each of the examples given, the weight of stabilizer additive falls within the aforementioned prescribed ranges, it being understood that all solvent will have been completely evaporated, or at least substantially so. As is well known in the art, other solvents than those illustrated will be found to work equally well, and the invention is not to be construed as limited to those solvents.

In the practice of our novel stabilized nitrocellulose film composition as a sealing material for the perforated recoilless rifle cartridge case, for example, the cartridge case will preferably be dipped into the composition but may be brushed or sprayed if the outer surfaces of the case have been provided with a prior thin vinyl webbing to serve as a base for our composition which also lends itself admirably well to shrink-fitted extruded seals over perforated cases. Whichever process be used, the case is now in condition to be dried at room temperature, the resulting case having a stabilized nitrocellulose film resistant to chemical and physical deterioration at ambient and elevated temperatures over extended periods of time. Further, our composition may be successfully employed to heat stabilize lacquers and the like having a nitrocellulose base.

It is well known by those skilled in the art that nitrocellulose chain breakdown is reflected in a corresponding decrease in viscosity of nitrocellulose in solution. It is also known that as nitrocellulose is denitrated, there is a corresponding viscosity decrease. The viscosity decrease of aged nitrocellulose film with time is, therefore, an indication of the degradation rate of nitrocellulose, reflecting both the loss of oxides of nitrogen and degree of polymer degradation. On aging at elevated temperatures of the order of F., the nitrocellulose, with the additives of our invention, showed a remarkable stability as indicated by its high resistance to viscosity decrease with time.

We claim:

1. A container for ammunition propellant comprising a dried stabilized nitrocellulose film composition resistant to temperatures upwardly of about 160 F. consisting essentially of a stabilizing compound selected from the group consisting of about 0.5 to 3.0% by Weight of 2- phenylphenol, 4-pheny1phenol, 4-4-dihydroxydiphenyl, 2-2-dihydroxypl1enyl, 2-4'-dihydroxydiphenyl and 2,5- di-t-butylhydroquinone, and about 1.0 to 4.0% of Z-benzyloxyphenol and 4benzyloxyphenol and the balance being substantially all nitrocellulose.

2. A container for ammunition propellant comprising a dried stabilized nitrocellulose film composition resistant to temperatures upwardly of about 160 F. consisting preferably of a stabilizing compound selected from the group consisting of about 1% by weight of 2-phenylphenol, 4-phenylphenol, 4-4-dihydroxydiphenyl, 2-2'-dihydroxydiphenyl, 2-4-dihydroxydiphenyl and 2,5-di-t- 5% butylhydroquinone and about 2% by weight of Z-benzyloxyphenol and 4-benzyloxyphenol and the balance being substantially all nitrocellulose.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Morawetz: Industrial and Engineering Chemistry, vol. 41. No. 7,. July 1949, pages 1142-1147. 

1. A CONTAINER FOR AMMUNITION PROPELLANT COMPRISING A DRIED STABILIZED NITROCELLULOSE FILM COMPOSITION RESISTANT TO TEMPERATURES UPWARDLY OF ABOUT 160*F. CONSISTING ESSENTIALLY OF A STABILIZING COMPOUND SELECTED FROM THE GROUP CONSISTING OF ABOUT 0.5 TO 3.0% BY WEIGHT OF 2PHENYLPHENOL, 4-PHENYLPHENOL, 4-4-DIHYDROXYDIPHENYL, 2-2''-DIHYDROXYPHENYL, 2-4''-DIHYDROXYDIPHENYL AND 2,5DI-T-BUTYLHYDROQUINONE, AND ABOUT 1.0 TO 4.0% OF 2-BENZYLOXYPHENOL AND 4-BENZYLOXYPHENOL AND THE BALANCE BEING SUBSTANTIALLY ALL NITROCELLULOSE. 